Various hard covers or shells (also known as hard tonneau covers) are commercially available for installation onto pickups or truck beds. These covers serve the purpose of keeping the contents of the truck bed out of view, protecting the cargo under the cover, are generally weather tight, and limit unauthorized entry into the truck bed when the cover is securely mounted.
Most hard covers are pivotally mounted to the front of the truck bed and open in clamshell-like fashion at the rear of the pickup bed. This is mechanically simple and durable, however, access to the front of the truck bed is severely restricted. Cargoes tend to shift forward in truck beds, hence items tend to migrate to the front of the truck bed where they are least accessible due to the smaller side opening as one approaches the front of the pickup bed where the cover is pivotally mounted. One obstacle with hard covers is that if the cargo extends above the side walls of the truck bed the cover cannot be closed. Another obstacle is that very large items, e.g., a refrigerator or welding machine, may not fit into the pickup bed and under such a cover that is hinged to the front pickup bed. In an attempt to solve some of these problems, a hard cover is described in U.S. Pat. No. 6,666,490 entitled “Pickup Bed Cover.” This cover rotatably raises the cover on four legs upward and backwardly to a fixed height and rear position. Although the cover increases the accessibility to the front of the pickup bed, it has the undesirable result in limiting the maximum cargo height. Also, loading access is impaired at the rear of the pickup bed because the cover is positioned into the loading area.
Another hard cover is described in U.S. Pat. No. 5,364,154 entitled “Liftable Rigid Truck Bed Cover.” This hard cover opens on four legs operating as a parallelogram. From the closed position, the cover lifts upward and rearward along the arc of the pivoting legs. This achieves good access to the pickup bed as mentioned above. However, the geometry of the opening and closing mechanism requires four latch points to secure the cover in the closed position. Also, the cover is positioned into an area that restricts loading access at the rear of the pickup bed.
Another type of hard cover is described in U.S. Pat. No. 4,673,209 entitled “Cover Assembly For Pickup Truck Bed.” The cover for the truck bed is mounted to the bed by four spring-loaded arms that allow the cover to be moved vertically relative to the bed. It has the advantage of increasing access to the entire truck bed. A disadvantage is the tedious opening and closing procedure which involves overcoming spring forces to raise and lower the cover at all four corners. Also, the cover must be manually locked into position in order to keep it positioned upright. Moreover, the covers require vertical stabilizers, which drop into the bed and may become entangled in the cargo when the cover is in the closed position.
Another type of cover is described in U.S. Pat. No. 6,767,043 entitled “Cover For Pick-Up Bed.” The cover is a shutter assembly that slides within a track assembly to open up the bed cover for hauling large cargo items in the truck bed. It has the undesirable feature that the cargo is not coverable while the large cargo item is in the truck bed.
It is clear that there is a need for an improved lift system for pickup bed covers that allows for variable height positioning for hauling cargo. Also, it is desirable to have a cover lift system that increases the access and ease by which cargo may be loaded into the bed of a pickup.